World War I

World War I was a global war fought from 28 July 1914 to 11 November 1918, during which 70,000,000 troops fought on the sides of the Triple Entente (United Kingdom, France, and Russia) and the Central Powers (German Empire, Austria-Hungary, and the Ottoman Empire). The war was fought across the world: France and Belgium in Western Europe; Poland, Belarus, and Ukraine in Eastern Europe; the Levant, Sinai Peninsula, Mesopotamia, and the Arabian Peninsula; the Pacific islands and the German port of Tsingtao (Qingdao) in China; the German colonies in Africa; and on the high seas. The war would end with an armistice and the punitive Treaty of Versailles, a peace agreement that divided the former territories of Germany, Turkey, and Austria into new countries and League of Nations mandates, and the former Central Powers nations were cut down to size. However, the war led to widespread changes across the world apart from weakening a few empires. The empires of Russia, Germany, Austria-Hungary, and Turkey all fell, nationalist sentiment increased across Europe'e new nations, Britain's domains sought greater self-rule, the United States became a great power, and the League of Nations was established.

Alliance systems
The "Scramble for Africa" and the other wars of the 1800s led to the establishment and expansion of great empires such as the United Kingdom, Russian Empire, France, Italy, the German Empire, Austria-Hungary, Japan, United States, and these powers created colonial empires with lands across the world, including Africa, East Asia, and the Pacific. Ever since the mid-19th century, Europe began to be divided into alliance systems, with Britain and France allying with the dying Ottoman Empire against Russia during the Crimean War, Prussia allying with Italy during the Italian Wars of Unification, and Britain and Japan allying after the Russo-Japanese War. By 1907, Europe had been divided into two major alliances: the Triple Entente of the United Kingdom, France, and Russia, and the Central Powers, an alliance between Germany, Austria, and Turkey. The Germans had been flexing their military muscles and had attempted to intervene in wars in Venezuela and Morocco, and they began an arms race against the British. The two countries competed for power in Europe, and the British allied with France and Russia to pit Germany against potential foes on both sides.

Balkan Wars
The 1910s saw the standoff come closer and closer to open conflict, and Western Europe appeared as if it was about to explode. However, World War I would start due to problems in the Balkans region of Eastern Europe. The late 19th and early 20th centuries saw the Ottoman Empire lose control of its possessions in the Balkans, with Bulgaria, Romania, Serbia, and Montenegro gaining their independence from the Turks with Russian assistance. Greece and these new nations allied against the Ottomans to seize Thrace, Rumelia, and Macedonia in the First Balkan War of 1912-1913, following a war between Italy and the Turks over Libya. The "Balkan League" seized most of the Ottoman Empire's remaining lands in Europe, but Bulgaria was disappointed with the land that it had received. Bulgaria would fight against its former allies in the Second Balkan War in 1913, only to be defeated. The Balkan tinderbox was close to being lit as multiple nations competed for control of the region.

Assassination of Franz Ferdinand
In 1907, Austria-Hungary annexed Bosnia and Herzegovina from the Ottoman Empire, angering the majority-Muslim population of the region, as well as several Serbs living in the region. The Black Hand, a secret society supported by Serbia, conducted a campaign of terrorism against the Austrians in Bosnia with the goal of creating an independent Bosnia and Herzegovina. On 28 June 1914, Black Hand member Gavrilo Princip assassinated Archduke Franz Ferdinand of Austria and his wife Sophie of Hohenburg in the Bosnian city of Sarajevo as they toured Austrian troops in the city. The killing of two Austrian royals by a Serb nationalist led to Austria-Hungary issuing an ultimatum to Serbia, demanding that Serbia should suppress nationalist movements in the country and execute the conspirators behind Franz Ferdinand's assassination. Austria-Hungary threatened to invade Serbia if the country did not accept the ultimatum by 28 July 1914, a month later. Serbia did not respond to these threats, so Austria-Hungary declared war on Serbia on 28 July 1914.

Declarations of war
Austria-Hungary was allied to the German Empire, which faithfully decided to assist its ally in its war with Serbia. Serbia was allied to Russia, which was the self-proclaimed defender of Orthodox Christianity in the Balkans, so Germany and Austria-Hungary also declared war on Russia. Russia was allied to France, so the Central Powers proceeded to declare war on France as well. The alliance systems of Europe finally met in a war, and Germany had to face enemies on two fronts. The Germans decided to enact the "Schlieffen Plan", a maneuver that would see German troops bypass the heavily-defended French border and invade France through neutral Belgium. Russia, a very large country, took a long time to mobilize its armies, and Austria-Hungary fought Serbia to a standstill. Germany did not have to worry about the Eastern Front in the first few weeks of the war, and the Germans decided to launch its invasion of Belgium and France.

Schlieffen Plan
On 2 August 1914, the German Empire requested military access to Belgium; on the same day, Germany peacefully occupied Luxembourg, whose 400-strong army was in no shape to resist the Imperial German Army. Belgium, a neutral country, refused to take sides in the war, and the United Kingdom professed its support for Belgian neutrality. On 4 August 1914, 750,000 German troops under Karl von Bulow and Alexander von Kluck invaded Belgium, facing the 220,000-strong Belgian army and the 247,400-strong British Expeditionary Force under General John French. The Germans reduced the fortresses of Namur and Liege, and Brussels fell to the Germans on 17 August 1914. The remnants of the Belgian army withdrew into Flanders and France, and the British were dealt horrible defeats at Mons and Le Cateau during the retreat.

German invasion of France
The Germans proceeded to drive deep into northern France, but they failed to beat the French and British forces to the English Channel in the "Race to the Sea", allowing for the French and British forces to form defensive lines. At the First Battle of the Marne in September 1914, the French and British put up a stiff defense not far from Paris, and they halted the German offensive with a decisive victory. The battle ended the Schlieffen Plan's successes, but the war degenerated into a series of trench battles and large-scale offensives by the German forces.

War with Russia
On 17 August 1914, the 800,000-strong Russian army launched an assault on the eastern German province of East Prussia, facing a mere 250,000 German troops under Paul von Hindenburg. The Russians were checked in battles at Stalluponen and Gumbinnen, but they would be dealt a fatal blow at the Battle of Tannenberg on 26-30 August 1914. The 230,000-strong Russian 2nd Army was wiped out, with 170,000 Russian troops being killed, wounded, or captured, and General Alexander Samsonov committed suicide after the defeat of his army. The Russians would again be defeated at the Masurian Lakes, making Hindenburg and his deputy Erich Ludendorff national heroes. The Russians fared better in Eastern Galicia against Austria-Hungary, and the Austro-Hungarians suffered from the problems surrounding poor leadership and ineffective training. Soon, the war on the Russian front would also turn into a stalemate.

All Quiet on the Western Front
As 1914 came to a close, the Germans were facing off against the French and British in northern France and in the Alsace and Lorraine regions of eastern France, and the opposing armies dug trenches and set up defensive positions. From 1915 to 1917, the two armies often engaged in trench warfare and massive offensives, including the bloody Battle of the Somme, the Battle of Verdun, and the Third Battle of Ypres. At Passchendaele, a part of the 1917 Battle of Ypres, mustard gas was used by both sides as chemical weapons, and several troops on both sides died in battle. These dreadful battles would continue until 1918, when the final offensives came from both sides.

The Middle East
The Ottoman Empire joined the war in October 1914 along with the other members of the Central Powers, although the empire did not play much of a role in the successes enjoyed by the alliance that year. Ottoman troops skirmished with British Army troops on the Sinai Peninsula of Egypt, fighting them in the desert. Britain and France decided that they could knock the Turks out of the war with one swift stroke, involving an invasion of the Dardanelles with naval forces. Allied ships bombarded cities such as Adrianople, but they were later forced to withdraw after facing heavy resistance. The most significant invasion of Turkey occurred on 25 April 1915 when 67,000 ANZAC troops from New Zealand and Australia landed on the Gallipoli Peninsula, assisting several thousand other troops from France, the UK, and other nations in the invasion. They were pinned down on the beaches for several months, and the Turkish general Mustafa Kemal (later known as "Mustafa Kemal Ataturk") became a war hero for defeating the Allies. In January 1916, after suffering immensely heavy losses, the Allies gave up the invasion, ending the chances of a quick war.

However, the British shifted their focus to the disaffected Arabs of the Levant and Mesopotamia, who were longing for a free Arab nation. The British sent T.E. Lawrence to advise the sheikhs of Hejaz to rise up against the Ottomans in the Arabian Peninsula and Levant, beginning the Arab Revolt. Arab irregulars, assisted by British armored cars, would drive the Turks out of Arabia, into the Levant, and would end the war in Damascus in late 1918. A British invasion of Mesopotamia at Kut failed, but the Arabs would succeed in liberating the Levant before the Ottoman surrender in October 1918.

Fall of the Eastern Front
The Austro-Hungarian Army on the Eastern Front, which had performed poorly, was soon subordinated to the Imperial German Army's high command. Hindenburg took command of the Central Powers forces on the Eastern Front, and the Germans destroyed a Russian army at the Gorlice-Tarnow Offensive in 1916. The Russian general Aleksei Brusilov decided to lead a massive counterattack against the Central Powers in Poland, and this "Brusilov Offensive" inflicted very high losses on the Austro-Hungarians. 1,325,000 Central Powers troops and 500,000 Russian troops were lost, and Brusilov was hailed as a hero. However, the political situation in Russia deteriorated as people became more aware of the corruption in Czar Nicholas II of Russia's government (including Grigory Rasputin's influence over the Czarina and Nicholas' failed military leadership), and the Germans made rapid progress in 1917 after the Russian Revolution toppled the czar. The Germans secured Riga in Latvia in September 1917, and they benefited from the fall of Aleksandr Kerensky's provisional government to the Bolsheviks in October 1917. In February-March 1918, the Germans launched a massive offensive in the Baltics, Ukraine, and Belarus after the Russian SFSR came to power, taking advantage of the Russian Civil War to seize large amounts of territory. In March 1918, the Soviets signed the Treaty of Brest-Litovsk, ending the war on the Eastern Front, and Germany set up various puppet nations in Eastern Europe.

End of the Western Front
Germany's huge successes during the war with the Russians were morale boosts for the Central Powers, but the Germans faced a new problem when they began to use "unrestricted submarine warfare" to attack enemy ships at sea. These tactics led to the sinking of several civilian ships, angering the United States, which lost several civilians aboard these ships. Germany agreed to the "Sussex Pledge", stating that it would halt this strategy. However, the Germans sunk RMS Lusitania on 7 May 1915, and the British intercepted an offer from the German government made to Mexico that proposed an anti-American alliance. In 1916, President Woodrow Wilson declared war on Germany, and the USA joined the Allies. In 1917, US troops began to arrive in France under John J. Pershing, but Pershing refused to let his men serve under British and French generals. In 1918, the American troops took part in battles at Belleau Wood and in the Meuse-Argonne Offensive, major offensives that saw several American troops die on European soil for the first time. The Germans began to suffer as more and more Allied troops arrived, and they launched the desperate "Spring Offensive" of 1918. This offensive was repelled, and the Allies barreled towards Belgium in the Hundred Days Offensive during the autumn of 1918. German troops began to mutiny, as did sailors at Kiel and Wilhelmshaven. In early November, the "November Revolution" began, and the German government began to lose control. On 11 November 1918, the Germans agreed to an armistice with the Allies, ending the war.